1. Field of the Invention
The invention relates to a fan and an impeller thereof, and more particularly to a quiet and highly efficient fan and an impeller thereof.
2. Description of the Related Art
As electronic devices are continuously improved, heat-dissipating devices and systems become increasingly important. Accumulation of heat reduces efficiency and may damage an electronic device. As integrated circuits continue to shrink and packaging is continuously developed to increase integration density, heat on each unit area of the integrated circuits increases. Thus, a heat-dissipating device with a high heat-dissipating efficiency must be developed.
Fans, a kind of a heat-dissipating device, are typically applied to electronic devices. Referring to FIGS. 1A and 1B, FIG. 1A is a schematic view showing a conventional impeller of a fan and FIG. 1B is a schematic view showing a blade of a conventional impeller installed at a setting angle. In FIG. 1A, the conventional impeller 12 includes a hub 121 and a plurality of blades 122 disposed around the hub 121. The blades 122 are typically installed around the hub 121 at an angle greater than 40 degrees in order to generate high pressure and large wind volume. FIG. 1B discloses that the setting angle θ1 at which the blade 122 is installed, is greater than 40 degrees.
When airflow passes through the blades 122, an inflow angle (θ1-θr1) is generated. Because the setting angle θ1 and the inflow angle (θ1-θr1) are overlarge, flow separation occurs at a suction surface of the blade, and then a turbulence is generated.
Pressure vibration caused by turbulence brings noise of boardband. Also, the overlarge setting angle θ1 increases the pressure variation at the surface of the blade 122, and then noise bandwidth and prominence ratio increases. In addition, because a conventional fan is driven by high electric current and speed stalls may occur early, a static pressure of an operating region of the fan decreases, and efficiency of the conventional fan is reduced. Thus, the conventional fan has disadvantages of consuming excessive power, generating excessive noise and having a low static pressure in an operating region.